Vinyl carbonyls, such as ethyl vinyl ketone, are important starting materials for the preparation of pharmaceutical and agricultural compounds. Because of their ability to react at either their carbonyl group or unsaturated position, vinyl carbonyls form a locus for the preparation of a wide variety of herbicides, pesticides, steroids, and medicines. However, vinyl carbonyls are not extensively used because they are expensive and not widely available.
Vinyl carbonyls, specifically ethyl vinyl ketone, form as a minor constituent from the Mannich reaction of methyl carbonyls, such as methyl ethyl ketone with formaldehyde (see F. F. Blicke; Organic Reactions, 1, 303 (1942); "The Mannich Reaction"). Other aldol condensations of methyl ethyl ketone with formaldehyde also form ethyl vinyl ketone usually as a minor contaminant in methyl isopropenyl ketone (please see U.S. Pat. Nos. 3,928,458 and 5,072,051 and E. M. McMahon, et al., Journal American Chemistry Society, 70, 2971 (1948), Preparation and Properties of Ethyl Vinyl Ketone and Methyl Isopropenyl Ketone). The difference in these preparations is the use of different aldol catalysts, sources of formaldehyde, and/or reaction conditions. However, no process produces significant quantities of vinyl carbonyls. Under the conditions of these publications the reactions lead to preponderant of the methyl isoalkenyl ketone, (i.e. methyl isopropenyl ketone). Attempting to increase the temperature to favor more equal amounts of the vinyl carbonyl rarely raises the amount much because heat also promotes the degradation of the vinyl carbonyls, reduces the catalyst activity, and/or decreases the selectivity. In most cases the mixture of methyl carbonyl reaction components is not acceptable. In fact, in some processes great lengths are made to ensure that only one isomer is present to start with. The standard preparation of pure ethyl vinyl ketone is the reaction of ethylene with propionyl chloride in nitromethane catalyzed by equimolar quantities of aluminum chloride (see R. B. Woodward, et al., Journal American Chemical Society, 74, 4223 (1952), The Total Synthesis of Steroids). In this case the yield of ethyl vinyl ketone is 22 percent. An improved yield of ethyl vinyl ketone comes from a four step synthesis starting with diethyl ketone (see B. Byrne, et al. Synth., 870 (1986), A Convenient Preparation of Ethyl Vinyl Ketone). In this case the yield of ethyl vinyl ketone is 67 percent. But in both cases the reactions consume equimolar quantities of expensive coreactants and produce copious amounts of waste products. For these reasons, neither reaction is suitable for manufacturing vinyl carbonyls.
Another reason why vinyl carbonyls are not widely available due to cost is the difficulty in the purification of the reaction components. Separating vinyl carbonyls and other reaction components, such as ethyl vinyl ketone from methyl isopropyl ketone is difficult because of the similar physical and chemical properties of the reaction products and the fact that they polymerize readily, especially in the presence of heat or bases.
Likewise, vinyl carbonyls are an unacceptable contaminant with the other reaction components such as isopropenyl ketone. One way to remove small amounts of ethyl vinyl ketone from methyl isopropenyl ketone uses strong base to selectively polymerize the ethyl vinyl ketone (see Japanese Patent Abstract 62142135 (1987).
It would be very desirable to be able to economically produce vinyl carbonyls. It would also be very desirable to economically produce vinyl carbonyls in essentially pure form by the purification of a mixture of reaction components.